New York -- Over the next 20 years some 60 million people in northern Africa are expected to leave the Sahelian region if desertification there is not halted, United Nations Secretary-General Kofi Annan said today. June 17 is the day set aside each year by the UN as World Day to Combat Desertification and Drought, twin problems that must be solved if world hunger is to be relieved, Annan said.

Desertification, environmental degradation and poverty are closely linked, and now an Australian scientist has found that air pollution may also play a role in the Sahel drought, by hampering the northward movement of the tropical rain belt.

Desertification and land degradation are worldwide phenomena with most severe effects on communities in the poorest rural areas. More than 110 countries are affected, and the livelihood of over 1.2 billion people are threatened by desertification, with 135 million around the world at risk of being displaced.

In northeast Asia, "dust and sandstorms have buried human settlements and forced schools and airports to shut down," Annan said, "while in the Americas, dry spells and sandstorms have alarmed farmers and raised the spectre of another Dust Bowl, reminiscent of the 1930s." In southern Europe, "lands once green and rich in vegetation are turning barren and brown," he said.

"Every year, an estimated $42 billion in income and six million hectares of productive land are being lost because of desertification, land degradation and declining agricultural productivity," Annan said today.

"The fight against desertification is fundamentally a fight against poverty," said Hama Arba Diallo, executive secretary of the eight year old UN Convention to Combat Desertification and Drought.

Diallo said that most of the 179 countries that are Parties to the convention are hosting activities today such as roundtable discussions, field trips and media campaigns at the national and local levels and involving government and nongovernmental organizations, the media, and other stakeholders.

But raising awareness of the problems is not enough - funds are needed to solve them. Diallo called on the international community to make financial commitments to enable countries affected by land degradation to implement the treaty.

"In order for the convention to move from preparation to the implementation of national action programmes, predictable financial resources are imperative," he said from the secretariat's office in Bonn, Germany.

He urged leaders of the international community who will be meeting at the Johannesburg World Summit for Sustainable Development in August and September to back up their pledges made 10 years ago at the UN Earth Summit in Rio de Janeiro.

Drought Air Pollution Link Found

Australian government researcher Dr. Leon Rotstayn has evidence that air pollution is likely to have contributed to the what he terms the "catastrophic drought in the Sahel," a region of northern Africa which borders the fringe of the Sahara Desert.

Tiny atmospheric particles, known as sulfate aerosol, have contributed to a global climate shift, he says.

"The Sahelian drought may be due to a combination of natural variability and atmospheric aerosol," says Dr. Rotstayn. "Cleaner air in future will mean greater rainfall in this region.

Atmospheric aerosol concentrations are far greater in the northern hemisphere, cooling the atmosphere there more than in the southern hemisphere. It is this imbalance that affects the tropical rain belt.

"Global climate change is not solely being caused by rising levels of greenhouse gases. Atmospheric pollution is also having an effect," says Dr. Rotstayn, who is affiliated with CSIRO, the Australian government's research branch.

CSIRO's research into aerosol and climate is in part supported by the Australian Greenhouse Office and involves collaboration with the University of Michigan in the USA and Dalhousie University in Canada. The findings on air pollution and the tropical rain belt have just been published in the international "Journal of Climate."

The researchers ran sophisticated global climate simulations on a supercomputer. They found that sulfate aerosol particles, which are concentrated mainly in the northern hemisphere, make cloud droplets smaller. This makes the clouds brighter and longer lasting, so they reflect more sunlight into space, cooling the Earth's surface below.

As a result, the tropical rain belt, which migrates northwards and southwards with the seasonal movement of the sun, is weakened in the northern hemisphere and does not move as far north.
The main impact of the weaker rain belt is in the Sahel. Since the 1960s, this region has experienced a devastating drought. Rainfall was 20 to 49 percent lower than in the first half of the 20th century, causing widespread famine and death.

Scientists also believe that air pollution over China has affected their summer monsoon rainfall belt. Northern China had successive droughts in the summers of 1997, 1998 and 1999.

A reduction in the severity of the Sahelian drought during the 1990s may be linked with emission controls in Europe and North America that lowered atmospheric aerosol concentrations during that decade, Dr. Rotstayn says.

Tropical and eastern Australia have experienced an increase in rainfall over the 20th century, and this may be related to the same effect.

"We are not yet seeing reductions in aerosol emissions in Asia," says Dr. Rotstayn. "It is possible that other forms of aerosol in the air, such as black soot emitted from Southeast Asia, could affect Australia's climate."

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